1. Field of the Invention
The present invention relates to a printing apparatus including an ink supply device such as an ink duct device, and more particularly to a technique for automatically adjusting the ink supply device.
2. Description of the Background Art
A typical offset printing apparatus includes a plurality of ink duct (or ink fountain) devices having ink keys, and can supply variable amounts of ink to respective segments extending across a predetermined feed direction of a paper sheet to be printed. This controls the amount of ink supply in accordance with the area of an image on a printing plate.
A conventional printing apparatus as described above has been adapted to measure the printed density and printed color on a printed paper sheet and to compare the measured printed density and the measured printed color with a preset target printed density and a preset target printed color, thereby effecting feedback control of the amount of ink supply.
The printing apparatus effecting the automatic control so that the measured printed density is approximately equal to the target printed density allows even an inexperienced operator to produce properly printed sheets.
There are, however, cases where a printed sheet is desired to be manually tint-corrected, for example, where it is desired that red is enhanced above normal in part of a finished printed sheet, based on the sensibilities of an operator or a designer. In such cases, the use of automatic setting makes it impossible to make partial adjustments.
The present invention is intended for a technique related to a printing apparatus including an ink supply device such as an ink duct device.
According to the present invention, a printing apparatus for applying ink to a printing medium while feeding the printing medium in a predetermined feed direction, thereby to provide a printed sheet, comprises: an ink supply mechanism for individually supplying a desired amount of ink through a plurality of ink transfer mechanisms to a plurality of regions defined on the printing medium to provide the printed sheet, each of the regions extending in the feed direction; a density setting element for setting a target printed density for all of the plurality of regions; an image reader provided in a feed path of the printed sheet for capturing an image on the printed sheet to obtain captured image data; an computation device for processing the captured image data to compute a measured printed density for each of the regions; a controller for controlling the amount of ink supplied from the ink supply mechanism for each of the regions so that the measured printed density is approximately equal to the target printed density; and a changing element for changing control by the controller in response to an instruction from an operator, whereby the controller controls the amount of ink supply to a selected one of the regions, based on the instruction from the operator.
This gives a higher priority to the conditions set by manual control and allows the conditions to be transferred to automatic control, thereby readily making partial tone changes and the like.
Preferably, the changing element includes a change key for changing the amount of ink supply for each of the regions in the designated proportion, whereby the controller changes the amount of ink supply to the selected region in the designated proportion each time the change key is manipulated.
Preferably, the changing element includes setting key for determining whether or not to cause the instruction to take effect for the controller.
It is therefore an object of the present invention to provide a printing apparatus capable of making a partial tone change while automatically controlling a printed density and, particularly, capable of reflecting manually set conditions in automatic settings.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.